Tribological characteristics of magnetorheological fluids based on carbonyl iron particles coated with various types of organosilanes

Magnetorheological fluids (MRFs) belong to the category of smart materials capable of reversibly altering their rheological behaviour under the influence of an external magnetic field. One of the most critical issues encountered in real-world applications, such as semi-active damping systems, is the long-term operational stability caused primarily by the excessive wear of the contact surfaces of the system. This study investigates the tribological and rheological behavior of magnetorheological fluids (MRFs) containing carbonyl iron particles (CIPs) coated with various organosilanes. The MRFs were prepared using CIPs coated with (3-aminopropyl)triethoxysilane (APTES), tetraethoxysilane (TEOS), vinyltrimethoxysilane (VTMS), and hexamethyldisilane (HMDS). Tribological experiments, conducted using a ball-on-disc configuration, demonstrated that organosilane-coated CIPs significantly improve the tribological characteristics compared to bare CIPs. The specific wear rate decreased from 3.393 × 10 −4 mm 3 N −1 m −1 for bare CIPs to 1.248 × 10 −4 mm 3 N −1 m −1 for HMDS-coated CIPs. The friction coefficient was also reduced, with HMDS-coated CIPs showing the lowest value. Rheological experiments revealed a direct correlation between shear viscosity and magnetic field strength, with organosilane-coated CIPs exhibiting lower viscosity and improved sedimentation stability. Among the coatings, HMDS showed the most significant reduction in wear and friction, attributed to the formation of a protective tribo-layer.